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Interference...
The physics of thin films and more...
Wave Superposition and Interference• What happens when waves meet?
• Path Difference - Phase Difference
2r
The Physics of Thin Films
• A Phase difference can occur because of…– path differences for different combining
wavetrains– phase shifts introduced under certain
reflections– go to applet thin film
Single, Double and Multi-Slit Interfence• Simple Case: Assume each slit acts as
a single source
• simulate this…– diffraction of water waves– thin slit diffraction
• The Grating Equation:
sinn d
Structural Colour in Plants and Animals
• The iridescent sheen of a bluebird wing or the extravagant colours of many butterflies and moths arise - not from chemistry (pigments) but from physics (interference effects)!!
The Physics of Structural Colour
• Light reflects from slightly different places along the surface. An optical path difference is introduced
Some colours work - some don’t...• The optical path
difference is just the extra distance that one ray travels wrt to an adjacent one. It’s easy to see that this leads to:
for constructive interference
2 / cosl n